karatelabs/karate · error

Expected string key in object

Error message

Expected string key in object

What it means

Within parseObject, every key must be a double-quoted string per RFC 8259. If after skipping whitespace the next character is not `"` (or input is exhausted), the parser throws "Expected string key in object". This rejects JS-style unquoted or single-quoted keys.

Solutions

1. Quote every object key with double quotes: `{"name": 1}`.
2. Convert single quotes around keys to double quotes.
3. Fix truncation so the object closes properly with `}` instead of ending where a key is expected.

Example fix

// before
var x = JSON.parse('{name: "a"}');

// after
var x = JSON.parse('{"name": "a"}');

// detect JS-style keys before parsing
if (/'[\w-]+'\s*:|(^|\{)\s*[A-Za-z_$][\w$]*\s*:/.test(input)) {
    throw new IllegalArgumentException('object keys must be double-quoted JSON strings');
}

try {
    var obj = JSON.parse(input);
} catch (e) {
    if (('' + e).indexOf('Expected string key') >= 0) {
        console.log('check that every object key is "quoted"');
    }
    throw e;
}

When it happens

Trigger: Parsing an object like `{name: 1}` (unquoted key), `{'name': 1}` (single-quoted key), or a truncated object `{"a":1,` where the parser expects the next key and hits `}` end-of-input.

Common situations: Hand-written JSON copied from JavaScript object literals; template-generated JSON with missing quotes; config files edited by hand and saved with JS-literal syntax.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

Related errors

• Unexpected token ' ' in JSON
• Expected ':' after object key
• Unexpected end of JSON input in object
• Unexpected end of JSON input in array
• Invalid number: bare '-'

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/5348ba3e20ce5687. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsonParser.java:115

                        return parseNumber();
                    }
                    throw syntaxError("Unexpected token '" + c + "' in JSON");
            }
        }

        private Map<String, Object> parseObject() {
            // we know s.charAt(pos) == '{'
            pos++;
            Map<String, Object> map = new LinkedHashMap<>();
            skipWs();
            if (pos < len && s.charAt(pos) == '}') {
                pos++;
                return map;
            }
            while (true) {
                skipWs();
                if (pos >= len || s.charAt(pos) != '"') {
                    throw syntaxError("Expected string key in object");
                }
                String key = parseString();
                skipWs();
                if (pos >= len || s.charAt(pos) != ':') {
                    throw syntaxError("Expected ':' after object key");
                }
                pos++;
                skipWs();
                Object value = parseValue();
                // RFC 8259: behavior of duplicate keys is unspecified; we keep
                // the last value (matches json-smart parseKeepingOrder).
                map.put(key, value);
                skipWs();
                if (pos >= len) {
                    throw syntaxError("Unexpected end of JSON input in object");
                }
                char c = s.charAt(pos);
                if (c == ',') {

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